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Planetary Glossary

Superjovian

A superjovian planet is any planet larger than Jupiter. Many superjovian planets have been discovered outside Earth's solar system, in part because superjovian planets are easier to detect than smaller planets. While there is no hard dividing line between superjovian planets and brown dwarf stars, anything above a mass of 15 Jupiters would likely be classed as a star.

Gas Giant

A gas giant (sometimes also known as a Jovian planet after the planet Jupiter) is a large planet that is not primarily composed of rock or other solid matter. Gas giants may have a rocky or metallic core—in fact, such a core is thought to be required for a gas giant to form—but the majority of its mass is in the form of gas (or gas compressed into a liquid state), mainly hydrogen and helium.

Supergiant Planet

A supergiant planet is a planet that is more massive than the largest cold mass, but less massive than a brown dwarf. These cold masses (not stars) are smaller in volume than the largest cold mass. All supergiant planets are also superjovian, meaning they are Superjupiters (more massive than Jupiter). Jupiter itself is close to having the mass of the largest cold mass.

Planemo

A planemo is a celestial object of planetary mass - one that is larger than an irregularly shaped asteroid, yet smaller than a nuclear reactive star. The term covers all bodies within this size range, although a planemo that orbits a star is more regularly referred to with the more specific term, planet. Planemo is a contraction of planetary mass object.